In reply to john arran:
A nicely executed theory.
A couple of confounders:
Firstly, the structure you apply assumes that grades are evenly-distributed - i.e. that there is the same gap HVS to E1 as from E6 to E7. I don't think that's true - in fact I think the "real" difficulty gap may be smaller further up but, because it's closer to the limit (a bit like measuring 1/1000ths of a second for pro sprinters instead of 1/10ths for amateurs).
Secondly, even if they were evenly spaced, the movement between them gets progressivly harder (think 10-minute miles to 5-minute miles).
Thirdly, I think the mix of people changes - from occasional weekend bumblies through to full-time professionals. Once people are in the E6+ arena, they are generally hugely motivated by climbing and also by the aim to get to the next level. Whereas others further down are very happy to bimble on HVS/E1 for the rest of their climbing careers.
Taking the above, I'd suggest that at least the 4th significant figure of your analysis may not be very significant...and probably the third, second and first too!